jdcochran
Member
OK, for my first post, I need a sanity check. For justifiable logistical reasons, I proposed to a client that I might be able to save them lots of FDA validation effort$ on a bar-code scanning operation to augment an existing line. How? By staying out of their existing PLC logic and adding an ancillary device/system that was not subject to extensive code validation and revision controls.
I proposed to accomplish this with a simple prox switch, simple relays, and some relay counters.
Now that I did it, I'm fearing that the line's high-speed indexing rate may byte me in the ASCII.
In essence, a small carton is scanned for pharmacode and compared with an expected result. If a bar code anomaly occurs, the product is rejected. Normally, it would be simple to immediately activate a reject function (in this case, a solenoid is activated). However, the reject action does not occur until later down the line, say 10 cycles later.
At any rate (no pun intended), I sketched out some prelim relay logic code. I have a few other logic decisions to make in the system... but ended up with a prox switch (for trigger), 2 counter relays, and 6 standard relays.
Questions:
1) what is the maximum rate at which todays off-the-shelf industrial relays (24VDC coil) typically respond?
2) in a PLC program, I must concerm myself with scanning sequence. In the hard-wired world, I must be concerned about everything happening at once. Any gotchas I need to consider before implementing a high-speed hard-wired relay system?
3) my line speed is somewhere between 400-600 clicks/min. Is this doable with discrete components? I'll even consider solid-state devices. Any suggestions on high-speed counters relays that could stand up to this speed? Discrete relays that can take the abuse?
I have a vision system as a contingency (has internal logic capability and runs at 3600/min rate). However, I'd like to present both options, the former being less expensive than the ladder.
[subtle PLC humor intended in previous statement]
Any assistance will be greatly appreciated and returned in kind.
-- John
I proposed to accomplish this with a simple prox switch, simple relays, and some relay counters.
Now that I did it, I'm fearing that the line's high-speed indexing rate may byte me in the ASCII.
In essence, a small carton is scanned for pharmacode and compared with an expected result. If a bar code anomaly occurs, the product is rejected. Normally, it would be simple to immediately activate a reject function (in this case, a solenoid is activated). However, the reject action does not occur until later down the line, say 10 cycles later.
At any rate (no pun intended), I sketched out some prelim relay logic code. I have a few other logic decisions to make in the system... but ended up with a prox switch (for trigger), 2 counter relays, and 6 standard relays.
Questions:
1) what is the maximum rate at which todays off-the-shelf industrial relays (24VDC coil) typically respond?
2) in a PLC program, I must concerm myself with scanning sequence. In the hard-wired world, I must be concerned about everything happening at once. Any gotchas I need to consider before implementing a high-speed hard-wired relay system?
3) my line speed is somewhere between 400-600 clicks/min. Is this doable with discrete components? I'll even consider solid-state devices. Any suggestions on high-speed counters relays that could stand up to this speed? Discrete relays that can take the abuse?
I have a vision system as a contingency (has internal logic capability and runs at 3600/min rate). However, I'd like to present both options, the former being less expensive than the ladder.
[subtle PLC humor intended in previous statement]
Any assistance will be greatly appreciated and returned in kind.
-- John
Last edited: